[Activity HAL] Added activity HAL source files

The activity_event_entry file is the implementation of the activity recognition
HAL, as described in hardware/libhardware/include/hardware/activity_recognition.h .

In order to test the HAL, run the activity test program. Running activity
without parameters will list a summary of the program usage.

Change-Id: I1717c3882340ec40016f303880e55b0b9bba45f8
Signed-off-by: Cristina Ciocan <cristina.ciocan@intel.com>
Reviewed-on: https://android.intel.com:443/331750